Optical imaging system

ABSTRACT

An optical imaging system includes a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, a fourth lens having a positive refractive power, a fifth lens having a negative refractive power, and a sixth lens having a negative refractive power. The first to sixth lenses are sequentially disposed from an object side to an imaging plane. An Abbe number of the second lens is 21 or less.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims benefit of priority under 35 U.S.C. § 119(a) toKorean Patent Application No. 10-2016-0174950 filed on Dec. 20, 2016 inthe Korean Intellectual Property Office, the disclosure of which isincorporated herein by reference in its entirety for all purposes.

BACKGROUND 1. Field

The present disclosure relates to an optical imaging system includingsix lenses.

2. Description of Related Art

Small camera modules may be mounted in mobile communications terminals.For example, small camera modules may be mounted in thin-width devices,such as mobile phones. Small camera modules include an optical imagingsystem including a small number of lenses and a small image sensor toallow for a thin width. For example, an optical imaging system in asmall camera module may include four or less lenses and an image sensorhaving a size of 7 millimeters (mm) or less.

However, because such optical imaging systems include a small number oflenses and an image sensor having a small size, it may be difficult forthe optical image sensor to be used in a small camera module having alow F number while maintaining high performance.

SUMMARY

This Summary is provided to introduce a selection of concepts, insimplified form, that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

According to an aspect of the present disclosure, an optical imagingsystem includes a first lens having a positive refractive power, asecond lens having a negative refractive power, a third lens having apositive refractive power, a fourth lens having a positive refractivepower, a fifth lens having a negative refractive power, and a sixth lenshaving a negative refractive power. The first to sixth lenses aresequentially disposed from an object side to an imaging plane. An Abbenumber of the second lens is 21 or less.

The first lens of the optical imaging system may have a convexobject-side surface along an optical axis and a concave image-sidesurface along the optical axis. The second lens of the optical imagingsystem can have a concave image-side surface along the optical axis. Thethird lens of the optical imaging system may have a convex object-sidesurface along the optical axis and a concave image-side surface alongthe optical axis.

The fourth lens of the optical imaging system can have a concaveobject-side surface along the optical axis and a convex image-sidesurface along the optical axis. The fifth lens of the optical imagingsystem may have a convex object-side surface along the optical axis anda concave image-side surface along the optical axis. One or moreinflection points can be formed on at least one of an object-sidesurface and an image-side surface of the fifth lens. The sixth lens ofthe optical imaging system may have a convex object-side surface alongthe optical axis and a concave image-side surface along the opticalaxis. One or more inflection points can be formed on at least one of anobject-side surface and an image-side surface of the sixth lens.

The optical imaging system can satisfy the expression S1S5/S1S11<0.365,where S1S5 represents a distance from an object-side surface of thefirst lens to an image-side surface of the third lens and S1S11represents a distance from the object-side surface of the first lens toan image-side surface of the sixth lens. The optical imaging system maysatisfy the expression R1/f<0.370, where R1 represents a radius ofcurvature of an object-side surface of the first lens and f representsan overall focal length of the optical imaging system along the opticalaxis.

The optical imaging system can satisfy the expression 30 mm<|f6|, wheref6 represents a focal length of the sixth lens. The optical imagingsystem may satisfy the expression 7.0 mm<2 ImgHT, where 2 ImgHTrepresents a diagonal length of an imaging plane. The optical imagingsystem can have an F number of less than 2.1. The optical imaging systemcan also satisfy the expression TTL/2 ImgHT<0.695, where TTL representsa distance from an object-side surface of a lens closest to the objectside among the first to sixth lenses to an imaging plane and 2 ImgHTagain represents a diagonal length of the imaging plane.

In another general aspect, an optical imaging system includes lensessequentially disposed from an object side to an imaging plane,satisfying the condition TTL/2 ImgHT<0.695. In the expression, TTLrepresents a distance from an object-side surface of a lens closest tothe object side among the plurality of lenses to an imaging plane and 2ImgHT represents a diagonal length of an imaging plane.

BRIEF DESCRIPTION OF DRAWINGS

The above and other aspects, features, and advantages of the presentdisclosure will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a view illustrating an optical imaging system according to afirst example;

FIG. 2 is a set of graphs representing aberration curves of the opticalimaging system illustrated in FIG. 1;

FIG. 3 is a table listing aspherical characteristics of the opticalimaging system illustrated in FIG. 1;

FIG. 4 is a view illustrating an optical imaging system according to asecond example;

FIG. 5 is a set of graphs representing aberration curves of the opticalimaging system illustrated in FIG. 4;

FIG. 6 is a table listing aspherical characteristics of the opticalimaging system illustrated in FIG. 4;

FIG. 7 is a view illustrating an optical imaging system according to athird example;

FIG. 8 is a set of graphs representing aberration curves of the opticalimaging system illustrated in FIG. 7; and

FIG. 9 is a table listing aspherical characteristics of the opticalimaging system illustrated in FIG. 7.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. However, various changes,modifications, and equivalents of the methods, apparatuses, and/orsystems described herein will be apparent after an understanding of thedisclosure of this application. For example, the sequences of operationsdescribed herein are merely examples, and are not limited to those setforth herein, but may be changed as will be apparent after anunderstanding of the disclosure of this application, with the exceptionof operations necessarily occurring in a certain order. Also,descriptions of functions and constructions that are well known may beomitted for increased clarity and conciseness.

The features described herein may be embodied in different forms, andare not to be construed as being limited to the examples describedherein. Rather, the examples described herein have been provided merelyto illustrate some of the many possible ways of implementing themethods, apparatuses, and/or systems described herein that will beapparent after an understanding of the disclosure of this application.

Although terms such as “first,” “second,” and “third” may be used hereinto describe various components, regions, or sections, these components,regions, or sections are not to be limited by these terms. Rather, theseterms are only used to distinguish one component, region, or sectionfrom another component, region, or section. Thus, a first component,region, or section referred to in examples described herein may also bereferred to as a second component, region, or section without departingfrom the teachings of the examples.

The terminology used herein is for describing various examples only, andis not to be used to limit the disclosure. The articles “a,” “an,” and“the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. The terms “comprises,” “includes,”and “has” specify the presence of stated features, numbers, operations,members, elements, and/or combinations thereof, but do not preclude thepresence or addition of one or more other features, numbers, operations,members, elements, and/or combinations thereof.

Due to manufacturing techniques and/or tolerances, variations of theshapes shown in the drawings may occur. Thus, the examples describedherein are not limited to the specific shapes shown in the drawings, butinclude changes in shape that occur during manufacturing.

The features of the examples described herein may be combined in variousways as will be apparent after an understanding of the disclosure ofthis application. Further, although the examples described herein have avariety of configurations, other configurations are possible as will beapparent after an understanding of the disclosure of this application.

In accordance with an example, a first lens refers to a lens closest toan object or a subject from which an image is captured. A sixth lens isa lens closest to an imaging plane or an image sensor. In an embodiment,all radii of curvature of lenses, thicknesses, a distance from anobject-side surface of a first lens to an imaging plane (OAL), a halfdiagonal length of the imaging plane (IMG HT), and focal lengths of eachlens are indicated in millimeters (mm). A person skilled in the relevantart will appreciate that other units of measurement may be used.Further, in embodiments, all radii of curvature, thicknesses, OALs(optical axis distances from the first surface of the first lens to theimage sensor), a distance on the optical axis between the stop and theimage sensor (SLs), image heights (IMGHs) (image heights), and backfocus lengths (BFLs) of the lenses, an overall focal length of anoptical system, and a focal length of each lens are indicated inmillimeters (mm). Further, thicknesses of lenses, gaps between thelenses, OALs, TLs, SLs are distances measured based on an optical axisof the lenses.

A surface of a lens being convex means that an optical axis portion of acorresponding surface is convex, and a surface of a lens being concavemeans that an optical axis portion of a corresponding surface isconcave. Therefore, in a configuration in which one surface of a lens isdescribed as being convex, an edge portion of the lens may be concave.Likewise, in a configuration in which one surface of a lens is describedas being concave, an edge portion of the lens may be convex. In otherwords, a paraxial region of a lens may be convex, while the remainingportion of the lens outside the paraxial region is either convex,concave, or flat. Further, a paraxial region of a lens may be concave,while the remaining portion of the lens outside the paraxial region iseither convex, concave, or flat. In addition, in an embodiment,thicknesses and radii of curvatures of lenses are measured in relationto optical axes of the corresponding lenses.

In accordance with illustrative examples, the embodiments described ofthe optical system include six lenses with a refractive power. However,the number of lenses in the optical system may vary, for example,between two to six lenses, while achieving the various results andbenefits described below. Also, although each lens is described with aparticular refractive power, a different refractive power for at leastone of the lenses may be used to achieve the intended result.

The present disclosure provides an optical imaging system capable ofbeing used in a small camera module while maintaining high performance.Hereinafter, embodiments of the present disclosure will be described indetail with reference to the accompanying drawings. Next, respectivelenses will be described in detail.

The first lens has a refractive power. For example, the first lens has apositive refractive power. One surface of the first lens may be convex.In an embodiment, an object-side surface of the first lens is convex.The first lens may have an aspherical surface. For example, bothsurfaces of the first lens are aspherical.

The first lens may be formed of a material having high lighttransmissivity and excellent workability. In an example, the first lensis formed of plastic. However, a material of the first lens is notlimited to plastic. In another example, the first lens may be formed ofglass.

The second lens has a refractive power. For example, the second lens hasa negative refractive power. One surface of the second lens may beconcave. In an embodiment, an image-side surface of the second lens isconcave. The second lens may have an aspherical surface. For example,both surfaces of the second lens are aspherical.

The second lens may be formed of a material having high lighttransmissivity and excellent workability. In an example, the second lensis formed of plastic. However, a material of the second lens is notlimited to plastic. In another example, the second lens may also beformed of glass. The second lens may have an Abbe number lower than thatof the first lens. In an embodiment, the Abbe number of the second lensmay be 21 or less.

The third lens has a refractive power. For example, the third lens has apositive refractive power. One surface of the third lens may be convex.In an embodiment, an object-side surface of the third lens is convex.The third lens may have an aspherical surface. For example, bothsurfaces of the third lens are aspherical.

The third lens may be formed of a material having high lighttransmissivity and excellent workability. In an example, the third lensis formed of plastic. However, a material of the third lens is notlimited to plastic. In another example, the third lens may be formed ofglass. The third lens may have an Abbe number lower than that of thefirst lens. In an embodiment, the Abbe number of the third lens is 21 orless.

The fourth lens has a refractive power. For example, the fourth lens hasa positive refractive power. One surface of the fourth lens may beconcave. In an embodiment, an object-side surface of the fourth lens isconcave. The fourth lens may have an aspherical surface. For example,both surfaces of the fourth lens are aspherical.

The fourth lens may be formed of a material having high lighttransmissivity and excellent workability. In an example, the fourth lensis formed of plastic. However, a material of the fourth lens is notlimited to plastic. In another example, the fourth lens may be formed ofglass. The fourth lens may have a refractive index lower than that ofthe third lens. In an embodiment, the refractive index of the fourthlens may be 1.6 or less.

The fifth lens has a refractive power. For example, the fifth lens has anegative refractive power. One surface of the fifth lens may be concave.In an embodiment, an image-side surface of the fifth lens may beconcave. The fifth lens may have an aspherical surface. For example,both surfaces of the fifth lens are aspherical. The fifth lens may haveinflection points. In embodiments, one or more inflection points areformed on an object-side surface and the image-side surface of the fifthlens.

The fifth lens may be formed of a material having high lighttransmissivity and excellent workability. In an example, the fifth lensis formed of plastic. However, a material of the fifth lens is notlimited to plastic. In another example, the fifth lens may be formed ofglass. The fifth lens may have a refractive index higher than that ofthe fourth lens. In an embodiment, the refractive index of the fifthlens is 1.65 or more.

The sixth lens has a refractive power. For example, the sixth lens has anegative refractive power. One surface of the sixth lens may be concave.In an embodiment, an image-side surface of the sixth lens is concave.The sixth lens may have inflection points. In embodiments, one or moreinflection points are formed on both surfaces of the sixth lens. Thesixth lens may have an aspherical surface. For example, both surfaces ofthe sixth lens are aspherical.

The sixth lens may be formed of a material having high lighttransmissivity and excellent workability. In an example, the sixth lensis formed of plastic. However, a material of the sixth lens is notlimited to plastic. In another example, the sixth lens may be formed ofglass.

The first to sixth lenses may have an aspherical shape, as describedabove. As an example, at least one surface of each of the first to sixthlenses is aspherical. Here, an aspherical surface of each lens may berepresented by the following Equation 1:

$\begin{matrix}{Z = {\frac{{cr}^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right)c^{2}r^{2}}}} + {Ar}^{4} + {Br}^{6} + {Cr}^{8} + {Dr}^{10} + {Er}^{12} + {Fr}^{14} + {Gr}^{16} + {Hr}^{18} + {{Jr}^{20}.}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Here, c represents an inverse of a radius of curvature of the lens, krepresents a conic constant, r represents a distance from a certainpoint on an aspherical surface of the lens to an optical axis, A to Jrepresent aspherical constants, and Z (or SAG) represents a distancebetween the certain point on the aspherical surface of the lens at thedistance r and a tangential plane meeting the apex of the asphericalsurface of the lens.

The optical imaging system may further include a stop. The stop may bedisposed between the first lens and the second lens or on theobject-side surface of the first lens.

The optical imaging system may further include a filter. The filter mayfilter partial wavelengths of light from incident light incident throughthe first to sixth lenses. For example, the filter is configured tofilter an infrared wavelength of the incident light.

The optical imaging system may further include an image sensor. Theimage sensor may provide the imaging plane on which light refracted bythe lenses may be imaged. For example, a surface of the image sensorforms the imaging plane. The image sensor may be configured to implementa high level of resolution. For example, the image sensor is configuredfor a unit size of pixels of 1.12 μm or less.

The optical imaging system may satisfy any one or any combination of anytwo or more of the following Conditional Expressions:2ImgHT>0.7 mm  [Conditional Expression 1]TTL/2ImgHT<0.695  [Conditional Expression 2]S1S5/S1S11<0.365  [Conditional Expression 3]R1/f<0.370  [Conditional Expression 4]30 mm<|f6|  [Conditional Expression 5]V2<21  [Conditional Expression 6]F No.<2.1.  [Conditional Expression 7]

Here, f represents an overall focal length of the optical imagingsystem, f6 represents a focal length of the sixth lens, V2 represents anAbbe number of the second lens, TTL represents a distance from theobject-side surface of the first lens to the imaging plane, 2 ImgHTrepresents the diagonal length of the imaging plane, R1 represents aradius of curvature of the object-side surface of the first lens, S1S5represents a distance from the object-side surface of the first lens toan image-side surface of the third lens, and S1S11 represents a distancefrom the object-side surface of the first lens to the image-side surfaceof the sixth lens.

Next, optical imaging systems according to several examples will bedescribed. First, an optical imaging system according to a firstembodiment will be described with reference to FIG. 1. The opticalimaging system 100 according to the first example includes lenses havingrespective refractive powers. For example, optical imaging system 100includes a first lens 110, a second lens 120, a third lens 130, a fourthlens 140, a fifth lens 150, and a sixth lens 160.

The first lens 110 has a positive refractive power. An object-sidesurface of lens 110 is convex and an image-side surface of lens 110 isconcave. The second lens 120 has a negative refractive power. Anobject-side surface of lens 120 is convex and an image-side surface oflens 120 is concave. The third lens 130 has a positive refractive power.An object-side surface of lens 130 is convex and an image-side surfaceof lens 130 is concave. The fourth lens 140 has a positive refractivepower. An object-side surface of lens 140 is concave and an image-sidesurface of lens 140 is convex.

The fifth lens 150 has a negative refractive power. An object-sidesurface of lens 150 is convex and an image-side surface of lens 150 isconcave. In addition, inflection points may be formed on the object-sidesurface and the image-side surface of fifth lens 150. For example, theobject-side surface of fifth lens 150 is convex in a paraxial region,and is concave in the vicinity of the paraxial region. Similarly, theimage-side surface of fifth lens 150 is concave in the paraxial region,and is convex in the vicinity of the paraxial region.

The sixth lens 160 has a negative refractive power. An object-sidesurface of lens 160 is convex and an image-side surface of lens 160 isconcave. In addition, inflection points may be formed on both surfacesof sixth lens 160. For example, the object-side surface of sixth lens160 is convex in the paraxial region, and is concave in the vicinity ofthe paraxial region. Similarly, the image-side surface of sixth lens 160is concave in the paraxial region, and is convex in the vicinity of theparaxial region.

Optical imaging system 100 includes a stop ST. For example, stop ST isdisposed between first lens 110 and second lens 120. Stop ST disposed asdescribed above controls an amount of light incident to an imaging plane180.

Optical imaging system 100 includes a filter 170. For example, filter170 is disposed between sixth lens 160 and imaging plane 180. Filter 170disposed as described above filters infrared light incident to imagingplane 180.

Optical imaging system 100 includes an image sensor. The image sensorprovides imaging plane 180 on which light refracted through the lensesis imaged. In addition, the image sensor may convert an optical signalimaged on imaging plane 180 into an electrical signal. In opticalimaging system 100, imaging plane 180 is formed at a significantly largesize. For example, a diagonal length of imaging plane 180 is greaterthan 7 mm. For reference, in an embodiment, the diagonal length (2ImgHT) of imaging plane 180 is 8.136 mm.

Optical imaging system 100 configured as described above has a low Fnumber. For example, the F number of optical imaging system 100according to an embodiment is 2.04.

Optical imaging system 100 exhibits aberration characteristics asillustrated by the graphs in FIG. 2. FIG. 3 is a table listingaspherical characteristics of optical imaging system 100.Characteristics of the lenses of optical imaging system 100 are listedin Table 1.

TABLE 1 F No. = 2.04 First Example FOV = 78.8 f = 4.873 TTL = 5.640Surface Radius of Thickness/ Abbe Focal No. Curvature Distance Index No.length S0 Stop −0.7213 S1 First Lens 1.7911 0.7208 1.546 56.11 3.825 S210.7380 0.1384 S3 Second Lens 117.3879 0.2511 1.667 20.35 −6.508 S44.1926 0.1544 S5 Third Lens 3.5007 0.3096 1.656 20.35 22.061 S6 4.45270.3149 S7 Fourth Lens −30.8531 0.5036 1.546 56.11 35.040 S8 −11.88400.5560 S9 Fifth Lens 6.7949 0.5890 1.656 20.35 −19.755 S10 4.3075 0.1864S11 Sixth Lens 1.8111 0.6362 1.536 55.66 −150.296 S12 1.5540 0.2795 S13Filter 0.2100 1.518 64.17 S14 0.7813 S15 Imaging 0.0090 Plane

An optical imaging system according to a second example will bedescribed with reference to FIG. 4. The optical imaging system 200according to the second embodiment may include lenses having respectiverefractive powers. For example, optical imaging system 200 includes afirst lens 210, a second lens 220, a third lens 230, a fourth lens 240,a fifth lens 250, and a sixth lens 260.

The first lens 210 has a positive refractive power. An object-sidesurface of lens 210 is convex and an image-side surface of lens 210 isconcave. The second lens 220 has a negative refractive power. Anobject-side surface of lens 220 is convex and an image-side surface oflens 220 is concave. The third lens 230 has a positive refractive power.An object-side surface of lens 230 is convex and an image-side surfaceof lens 230 is concave. The fourth lens 240 has a positive refractivepower. An object-side surface of lens 240 is concave and an image-sidesurface of lens 240 is convex.

The fifth lens 250 has a negative refractive power. An object-sidesurface of lens 250 is convex and an image-side surface of lens 250 isconcave. In addition, inflection points may be formed on the object-sidesurface and the image-side surface of fifth lens 250. For example, theobject-side surface of fifth lens 250 is convex in a paraxial region,and is concave in the vicinity of the paraxial region. Similarly, theimage-side surface of fifth lens 250 is concave in the paraxial region,and is convex in the vicinity of the paraxial region.

The sixth lens 260 has a negative refractive power. An object-sidesurface of lens 260 is convex and an image-side surface of lens 260 isconcave. In addition, inflection points may be formed on both surfacesof sixth lens 260. For example, the object-side surface of sixth lens260 is convex in the paraxial region, and is concave in the vicinity ofthe paraxial region. Similarly, the image-side surface of sixth lens 260is concave in the paraxial region, and is convex in the vicinity of theparaxial region.

Optical imaging system 200 includes a stop ST. For example, stop ST isdisposed between first lens 210 and second lens 220. Stop ST disposed asdescribed above controls an amount of light incident to an imaging plane280.

The optical imaging system 200 includes a filter 270. For example,filter 270 is disposed between sixth lens 260 and imaging plane 280.Filter 270 disposed as described above filters infrared light incidentto imaging plane 280.

Optical imaging system 200 may include an image sensor. The image sensorprovides imaging plane 280 on which light refracted through the lensesis imaged. In addition, the image sensor may convert an optical signalimaged on imaging plane 280 into an electrical signal. In an embodiment,imaging plane 280 may be formed at a significantly large size. Forexample, a diagonal length of imaging plane 280 is greater than 7 mm.For reference, in the described embodiment, the diagonal length (2ImgHT) of imaging plane 280 is 8.136 mm.

The optical imaging system 200 configured as described above may have alow F number. For example, the F number. of the optical imaging systemaccording to the described embodiment is 2.04.

The optical imaging system according to an embodiment exhibitsaberration characteristics as illustrated by the graphs in FIG. 5. FIG.6 is a table listing aspherical characteristics of optical imagingsystem 200. Characteristics of the lenses of optical imaging system 200are listed in Table 2.

TABLE 2 F No. = 2.04 Second Example FOV = 78.8 f = 4.873 TTL = 5.640Surface Radius of Thickness/ Abbe Focal No. Curvature Distance Index No.length S0 Stop −0.7210 S1 First Lens 1.7893 0.7159 1.546 56.11 3.815 S210.8443 0.1390 S3 Second Lens 240.9604 0.2461 1.667 20.35 −6.578 S44.3181 0.1533 S5 Third Lens 3.5966 0.2990 1.656 20.35 22.924 S6 4.56820.3077 S7 Fourth Lens −23.2767 0.5075 1.546 56.11 34.250 S8 −10.45480.5725 S9 Fifth Lens 6.9081 0.5927 1.656 20.35 −22.182 S10 4.5280 0.1854S11 Sixth Lens 1.8469 0.6366 1.536 55.66 −65.986 S12 1.5440 0.3200 S13Filter 0.2100 1.518 64.17 S14 0.7457 S15 Imaging 0.0086 Plane

An optical imaging system according to a third example will be describedwith reference to FIG. 7. The optical imaging system 300 according tothe embodiment includes lenses having respective refractive powers. Forexample, optical imaging system 300 includes a first lens 310, a secondlens 320, a third lens 330, a fourth lens 340, a fifth lens 350, and asixth lens 360.

The first lens 310 has a positive refractive power. An object-sidesurface of lens 310 is convex and an image-side surface of lens 310 isconcave. The second lens 320 has a negative refractive power. Bothsurfaces of lens 320 are concave. The third lens 330 has a positiverefractive power. An object-side surface of lens 330 is convex and animage-side surface of lens 330 is concave. The fourth lens 340 has apositive refractive power. An object-side surface of lens 340 is concaveand an image-side surface of lens 340 is convex.

The fifth lens 350 has a negative refractive power. An object-sidesurface of lens 350 is convex and an image-side surface of lens 350 isconcave. In addition, inflection points may be formed on the object-sidesurface and the image-side surface of fifth lens 350. For example, theobject-side surface of fifth lens 350 is convex in a paraxial region,and is concave in the vicinity of the paraxial region. Similarly, theimage-side surface of fifth lens 350 is concave in the paraxial region,and is convex in the vicinity of the paraxial region.

The sixth lens 360 has a negative refractive power. An object-sidesurface of lens 360 is convex and an image-side surface of lens 360 isconcave. In addition, inflection points may be formed on both surfacesof sixth lens 360. For example, the object-side surface of sixth lens360 is convex in the paraxial region, and is concave in the vicinity ofthe paraxial region. Similarly, the image-side surface of sixth lens 360is concave in the paraxial region, and is convex in the vicinity of theparaxial region.

Optical imaging system 300 includes a stop ST. For example, Stop ST isdisposed on the object-side surface of first lens 310. Stop ST disposedas described above controls an amount of light incident to an imagingplane 380.

Optical imaging system 300 includes a filter 370. For example, filter370 is disposed between sixth lens 360 and imaging plane 380. Filter 370disposed as described above filters infrared light incident to imagingplane 380.

Optical imaging system 300 includes an image sensor. The image sensorprovides imaging plane 380 on which light refracted through the lensesis imaged. In addition, the image sensor may convert an optical signalimaged on imaging plane 380 into an electrical signal. In an embodiment,imaging plane 380 is formed at a significantly large size. For example,a diagonal length of the imaging plane 380 is greater than 7 mm. Forreference, in optical imaging system 300, the diagonal length (2 ImgHT)of imaging plane 380 is 8.136 mm.

Optical imaging system 300 configured as described above may have low Fnumber. For example, the F number of optical imaging system 300according to an embodiment is 2.08.

Optical imaging system 300 exhibits aberration characteristics asillustrated by the graphs in FIG. 8. FIG. 9 is a table listingaspherical characteristics of the optical imaging system according to anembodiment. Characteristics of the lenses of optical imaging system 300are listed in Table 3.

TABLE 3 F No. = 2.08 Third Example FOV = 78.8 f = 4.874 TTL = 5.622Surface Radius of Thickness/ Abbe Focal No. Curvature Distance Index No.length S0 Stop −0.4221 S1 First Lens 1.6967 0.7664 1.546 56.11 3.660 S29.3957 0.1052 S3 Second Lens −17.4231 0.2307 1.667 20.35 −7.478 S47.0505 0.1466 S5 Third Lens 4.3247 0.3351 1.656 20.35 23.011 S6 5.86990.3023 S7 Fourth Lens −28.9448 0.4570 1.546 56.11 194.468 S8 −22.87600.4661 S9 Fifth Lens 104.5584 0.6603 1.656 20.35 −20.989 S10 12.15870.1362 S11 Sixth Lens 2.4000 0.8006 1.536 55.66 −33.521 S12 1.87080.2100 S13 Filter 0.2100 1.518 64.17 S14 0.7757 S15 Imaging 0.0200 Plane

Table 4 lists values of Conditional Expressions of the optical imagingsystems according to the first to third examples. As seen in Table 4,optical imaging systems 100, 200 and 300 satisfy all of the numericalranges of the Conditional Expressions disclosed in the detaileddescription of the present application.

TABLE 4 Conditional Expression 1st Example 2nd Example 3rd ExampleTTL/2ImgHT 0.6932 0.6932 0.6910 S1S5/S1S11 0.3610 0.3566 0.3595 R1/f0.3676 0.3672 0.3481 |f6| 150.296 65.986 33.521 V2 20.3532 20.353220.3532

As set forth above, according to the embodiments in the presentdisclosure, an optical imaging system can be implemented that isappropriate for a small camera module while still having highperformance.

While embodiments have been shown and described above, it will beapparent to those skilled in the art that modifications and variationscould be made without departing from the scope of the presentapplication as defined by the appended claims.

What is claimed is:
 1. An optical imaging system comprising: a firstlens comprising a positive refractive power; a second lens comprising anegative refractive power; a third lens comprising a positive refractivepower; a fourth lens comprising a positive refractive power; a fifthlens comprising a negative refractive power; and a sixth lens comprisinga negative refractive power, wherein the first to sixth lenses aresequentially disposed from an object side to an imaging plane, andwherein TTL/2ImgHT<0.695 in which TTL represents a distance from anobject-side surface of a lens closest to the object side among the firstto sixth lenses to an imaging plane and 2ImgHT represents a diagonallength of the imaging plane.
 2. The optical imaging system of claim 1,wherein an object-side surface of the first lens is convex along anoptical axis, and an image-side surface of the first lens is concavealong the optical axis.
 3. The optical imaging system of claim 1,wherein an image-side surface of the second lens is concave along anoptical axis.
 4. The optical imaging system of claim 1, wherein anobject-side surface of the third lens is convex along an optical axis,and an image-side surface of the third lens is concave along the opticalaxis.
 5. The optical imaging system of claim 1, wherein an object-sidesurface of the fourth lens is concave along an optical axis, and animage-side surface of the fourth lens is convex along the optical axis.6. The optical imaging system of claim 1, wherein an object-side surfaceof the fifth lens is convex along an optical axis, and an image-sidesurface of the fifth lens is concave along the optical axis.
 7. Theoptical imaging system of claim 1, wherein one or more inflection pointsare formed on at least one of an object-side surface or an image-sidesurface of the fifth lens.
 8. The optical imaging system of claim 1,wherein an object-side surface of the sixth lens is convex along anoptical axis, and an image-side surface thereof is concave along theoptical axis.
 9. The optical imaging system of claim 1, wherein one ormore inflection points are formed on at least one of an object-sidesurface or an image-side surface of the sixth lens.
 10. The opticalimaging system of claim 1, wherein S1S5/S1S11<0.365 in which S1S5represents a distance from an object-side surface of the first lens toan image-side surface of the third lens and S1S11 represents a distancefrom the object-side surface of the first lens to an image-side surfaceof the sixth lens.
 11. The optical imaging system of claim 1, whereinR1/f<0.370 in which R1 represents a radius of curvature of anobject-side surface of the first lens and f represents an overall focallength of the optical imaging system along the optical axis.
 12. Theoptical imaging system of claim 1, wherein 30 mm<|f6| in which f6represents a focal length of the sixth lens.
 13. The optical imagingsystem of claim 1, wherein 7.0 millimeters (mm)<2ImgHT, where 2ImgHTrepresents a diagonal length of an imaging plane.
 14. The opticalimaging system of claim 1, wherein an F number of the optical imagingsystem is less than 2.1.
 15. The optical imaging system of claim 1,wherein an Abbe number of the second lens is 21 or less.